This section provides background information to facilitate a better understanding of the various aspects of the disclosure. It should be understood that the statements in this section of this document are to be read in this light, and not as admissions of prior art.
Many rubber articles, such as conveyor belts, automobile tires, hoses, power train belts, e.g., transmission belts, and the like, are usually reinforced with fibrous or metal cords. In all such instances, the fiber or metal cord must be firmly bonded to the rubber. This is so whether the fiber or cord is a natural or synthetic polymer, or metallic, and whether the rubbers are natural or synthetic.
Conventional conveyor belts which are used in heavy duty applications are typically comprised of a cured rubber or polyvinyl chloride (PVC) based material as a top layer, a cured rubber or PVC based material as a bottom layer, and one or more reinforcement layers (a carcass) disposed between the top layer and the bottom layer. The cured rubber or polyvinyl chloride based material may also serve to adhere various components of the reinforcing carcass. For example, individual layers and reinforcing elements included in the carcass may be encapsulated in a matrix of polymeric elastomeric resin, such as a polyvinylchloride based material. The individual layers are commonly saturated with the liquid elastomer-forming polymeric resin prior to being joined together, and the reinforcing elements may be inserted, for example, by tufting, sewing, or stitch-bonding. In cases where the liquid saturate is a polyvinylchloride plastisol, the resin is gelled, or otherwise cured, by application of heat.
Some conveyor belts contain reinforcement elements which include zinc coated steel cords. Conveyor belts of these types can offer excellent performance characteristics and a relatively long service life. However, under some conditions where the conveyor belts are exposed to repeated high temperatures and/or humidity over long periods of time, the zinc coated steel cord reinforcements can delaminate, or otherwise lose adhesion, from the rubber matrix of the conveyor belt.
For bonding the rubber to the zinc coated steel cord surface, special rubber formulations have been known to be used in the form of adhesion compounds. One solution to provide protection against aging/corrosion and loss of adhesion has been addition of lead oxide (PbO). However, PbO is considered a hazardous substance and is rated as SVHC substance in the REACH regulation, which could ultimately be banned for use. Also, currently available alternative compounds without PbO can achieve good adhesion to the cord surface, but the generated bonding is more susceptible to aging/corrosion than with compounds containing PbO.
Thus, there is an ongoing need for conveyor belts including zinc coated steel cordage with improved bonding between the zinc coated steel cord surface and rubber matrix, while be exposed to thermal and/or humidity aging conditions, such need met, at least in part, with embodiments according to the following disclosure.